1. Field of the Invention
Exemplary embodiments of the present invention relate to a communication system; and, more particularly, to an apparatus and method for encoding a voice and audio signal by expanding a modified discrete cosine transform (MDCT) based CODEC to a wideband and a super-wideband in a communication system.
2. Description of Related Art
There have many studies actively made to provide services with various Quality of Services (QoS) at a high transmit rate in a communication system. Further, many methods have been introduced to transmit data at a high transmit rate with various QoSs through limited resources in such a communication system. Due to the advance of network technology and the increment of user demand for high quality services, methods for providing a high quality service through a wideband and a super wideband from a narrowband have been introduced.
Furthermore, a bandwidth for transmitting voice and audio in a network has been increased due to the development of a communication technology. It causes the increment of user demands for high quality services through highband voice and audio such as a music streaming service. In order to satisfy such a user demand, a method for compressing and transmitting a high quality voice and audio signal has been introduced.
Meanwhile, various methods for encoding corresponding data to provide various QoS services to users through a wideband and a super wideband have been introduced in a communication system. Particularly, various encoding types of CODECs have been introduced to stably process and transmit data in a high transmit rate. An encoder for encoding data using such CODEC performs an encoding process by a layer, and each layer is separated by a frequency band.
The encoder performs an encoding operation per each band signal of each layer. For example, when the encoder encodes a voice and audio signal, the encoder independently encodes a lowband signal and a highband signal. Particularly, in order to effectively compress and transmit high quality voice and audio signals for providing a high quality voice and audio service to a user, the encoder divides a wideband signal and a super wideband signals into multiples subband signals and independently encodes the multiple subband signals.
The independently coded highband signal has a bit rate similar to that of a lowband signal. After receiving the independently coded highband signal, a receiver restores a lowband signal first and restores a highband signal using the restored lowband signal. The restored lowband signal and the restored highband signal are restored through gain compensation based on an original signal. For the gain compensation in the receiver, the transmitter encodes gain information of the lowband signal and the highband signal and transmits the encoded gain information to the receiver. The receiver performs the gain compensation operation using the encoded gain information transmitted from the transmitter when the encoded lowband and highband signals are restored. Therefore, the encoder of the transmitter independently encodes a voice and audio signal by each band of each layer, encodes the gain information of the voice and audio signal at a bandwidth extension (BWE) layer, and transmit the encoded voice and audio signal with the encoded gain information to the receiver.
However, there is a problem in restoration of the encoded voice and audio signal using the gain information encoded at the BWE layer when the encoder divides a wideband and a super wideband to multiple subbands and independently performs the encoding operation for providing the high quality voice and audio service. In other words, there is a problem in gain compensation of a restored highband signal using gain information encoded at a BWE layer after the receiver restores the highband signal using a restored lowband signal. When the receiver restores the highband signal using the restored lowband signal and uses the gain information encoded at the BWE layer for gain compensation of the restored highband signal, a gain-compensated signal has an error because the encoded gain information does not indicate a real gain of each band, particularly, a real gain of a highband. Such an error causes deteriorating audio quality.
That is, such a gain mismatch problem is generated at a band boundary of the divided subbands by performing the gain compensation operation per each divided subband using the encoded gain information when the gain compensation operation is performed for restoring the encode signal. The gain mismatch problem deteriorates the audio quality.
Therefore, there has been a demand for developing a method for encoding a voice and audio signal by expanding a related CODEC to a wideband and a super wideband in order to provide a high quality voice and audio signal through a wideband and a super wideband in a communication system.